Center beam rail road cars, in cross-section, generally have a body having a flat car deck and a center beam web structure running along the longitudinal center-line of, and standing upright from, the deck. The center beam structure is carried on a pair of rail car trucks. The rack, or center beam structure, has a pair of bulkheads at either longitudinal end that extend transversely to the rolling direction of the car. The lading supporting structure of the beam includes laterally extending deck sheets or bunks mounted above, and spanning the space between, the trucks. The center beam web structure is typically in the nature of an open frame truss for carrying vertical shear and bending loads. It stands upright from the deck and runs along the longitudinal centerline of the car between the end bulkheads. This kind of webwork structure can be constructed from an array of parallel uprights and appropriate diagonal bracing. Most often, a top truss assembly is mounted on top of the vertical web and extends laterally to either side of the centerline of the car. The top truss is part of an upper beam assembly, (that is, the upper or top flange end of the center beam) and is usually manufactured as a wide flange, or wide flange-simulating truss, both to co-operate with the center sill to resist vertical bending, and also to resist bending due to horizontal loading of the car while travelling on a curve. Typically, a center sill extends the length of the car. The center beam thus formed is conceptually a deep girder beam whose bottom flange is the center sill, and whose top flange is the top truss (or analogous structure) of the car.
Center beam cars are commonly used to transport packaged bundles of lumber, although other loads such as pipe, steel, engineered wood products, or other goods can also be carried. The space above the decking and below the lateral wings of the top truss on each side of the vertical web of the center beam forms left and right bunks upon which bundles of wood can be loaded. The base of the bunk often includes risers that are mounted to slant inward, and the vertical web of the center beam is generally tapered from bottom to top, such that when the bundles are stacked, the overall stack leans inward toward the longitudinal centerline of the car.
Lading is most typically secured in place using straps or cables. Generally, the straps extend from a winch device mounted at deck level, upward outside the bundles, to a top fitting. The top fitting can be located at one of several intermediate heights for partially loaded cars. Most typically, the cars are fully loaded and the strap terminates at a fitting mounted to the outboard wing of the upper beam assembly. Inasmuch as the upper beam assembly is narrower than the bundles, when the strap is drawn taut by tightening the winch, it binds on the upper outer corner of the topmost bundle and exerts a force inwardly and downwardly, tending thereby to hold the stack in place tight against the center beam web.
Each bundle typically contains a number of pieces of lumber, commonly the nominal 2″×4″, 2″×6″, 2″×8″ or other standard size. The lengths of the bundles vary, typically ranging from 8′ to 24′, in 2′ increments. The most common bundle size is nominally 32 inches deep by 49 inches wide, although 24 inch deep bundles are also used, and 16 inch deep bundles can be used, although these latter are generally less common. A 32 inch nominal bundle may contain stacks of 21 boards, each 1-½ inch thick, making 31-½ inches, and may include a further 1-½ inches of dunnage for a total of 33 inches. The bundles are loaded such that the longitudinal axes of the boards are parallel to the longitudinal, or rolling, axis of the car generally. The bundles are often wrapped in a plastic sheeting to provide some protection from rain and snow, and also to discourage embedment of abrasive materials such as sand, in the boards. The bundles are stacked on the car bunks with the dunnage located between the bundles such that a fork-lift can be used for loading and unloading. For bundles of kiln dried softwood lumber the loading density is typically taken as being in the range of 1600 to 2000 Lbs. per 1000 board-feet.
It has been observed that when the straps are tightened, the innermost, uppermost boards of the topmost bundle bear the greatest portion of the lateral reaction force against the center beam due to the tension in the straps or cables. It has also been observed that when these bundles bear against the vertical posts of the center beam, the force is borne over only a small area. As the car travels, it is subject to vibration and longitudinal inertia loads. Consequently the plastic sheeting may tend to be torn or damaged in the vicinity of the vertical posts, and the innermost, uppermost boards can be damaged. The physical damage to these boards may tend to make them less readily saleable. Further, whether or not the boards are damaged, if the plastic is ripped, moisture can collect inside the sheeting. This may lead to the growth of molds, and may cause discoloration of the boards. In some markets the aesthetic appearance of the wood is critical to its saleability, and it would be advantageous to avoid this discoloration.
In part, the difficulty arises because the bearing area against the posts may tend to be too small. Further, the join between the upstanding web portion of the center beam and the upper beam assembly can coincide with the height of the topmost boards. This join is not always smooth. Further still, when the posts are fabricated the flanges may not stand perfectly perpendicular to the web, such that one edge of the flange may bear harder against the bundles than another. It would be advantageous to present a larger, smoother, and more homogenous surface to the bundles, or to reduce the force acting at the interface between the bundles and the beam. Use of a roll-formed section, as opposed to a fabricated (i.e., welded) flange assembly may tend to increase the probability that the facing part will be oriented correctly, will tend to have appropriately planar surfaces with smoothly radiused corners, and will tend to present fewer asperities (such as may otherwise arise with distortion and errors in welding) to the lading. Use of smoothly radiused posts, such as can be obtained with roll-formed sections, whether channel or structural tubes for the vertical posts may tend to be advantageous in this regard. Use of a smooth longitudinal beam, whether channel, rectangular tube, or square tube, of somewhat greater outside dimension than the vertical posts may also tend to be advantageous as the quality of the primary bearing surface, namely the longitudinal chord surface rather than the vertical post surface, will be determined by the quality and consistency of the roll-forming process, typically quite high, as opposed to the quality and repeatability of a manual welding process, typically much lower by comparison.
Existing center beam cars tend to have been made to fall within the car design envelope, or outline, of the American Association of Railroads standard AAR Plate C, and tend to have a flat main deck that runs at the level of the top of the main bolsters at either end of the car. In U.S. Pat. No. 4,951,575, of Dominguez et al., issued Aug. 28, 1990, a center beam car is shown that falls within the design envelope of plate C, and also has a depressed center deck between the car trucks. It would be advantageous to be able to operate center beam cars that exceed Plate C and fall within AAR Plate F, with a full load of lumber in bundles stacked 5 bundles high. A five bundle high load of 33 inch bundles requires a vertical clearance in the left and right hand bunks of at least 165 inches. This significantly exceeds the vertical loading envelope of a plate C car.
Increased vertical loading to exceed Plate C, as in a Plate F car, may tend also to increase the height of the center of gravity of a loaded car above the allowable vertical center of gravity height limit of 98 inches measured from top-of-rail (TOR). Consequently it may be desired to drop the center portion of the deck further to once again lower the center of gravity. However, as the deck is dropped further, the deck must also become narrower to remain within the AAR design envelope, whether of Plate C or Plate F. Further still, when the truck centers of the car exceed 46 ft. 3 in., the mid-span car width must be reduced due to swing out as the car travels through corners. That is, the car must lie within the design envelope of a 10--8″ wide car with 46--3″ truck centers, on a 13° curve (equivalent to a track center radius of 441.7 ft.). A car having a nominal length of 73 ft, and a 40′-6″ well, will tend to have a distance between truck centers of the order of 56 to 60 ft. The allowance for swing out, (that is, the reduction in width to match a car having 46′-3″ truck centers), for such a car is significant.
As the allowable car width becomes narrower, either due to increasing the truck centers beyond 46 ft. 3 in., or due to lowering the height of the decking, it is highly desirable to retain as much of the remaining lateral width as possible to support the bundles. Moreover, it has become desirable to provide a bunk width sufficient to carry 51 inch wide bundles, as well as 49 inch wide bundles. In the past, as shown in U.S. Pat. No. 4,951,575 winches have been installed outboard of the side sills at longitudinal stations corresponding to the longitudinal stations of the outboard ends of the cross bearers. These winches are used to cinch the strapping that is used to secure the load to the center beam top compression member wings, or, in the case of a partially loaded car, to the center beam main vertical web assembly. The winches tend to extend further laterally outboard, relative to the longitudinal centerline, than any other part of the car. Given the inwardly angled profile of the lower portions of the Plate C and Plate F envelopes, each incremental decrease in overall car width measured from the centerline to the outboard extremity of the winch permits an incremental lowering of the loaded center of gravity of the car. Consequently, it is advantageous to make the winch mounting as laterally compact as possible.
Further, given that the allowable width of the car decreases as truck center distance increases, and given that the allowable width envelope is fixed for a given truck center distance, for cars in which the center sill extends above the lading interface of at least a portion of the decking structure, as is the case in a dropped deck center beam car, another way of widening the effective bunk width on which to carry lading is to employ a relatively narrow center sill. However, the width of the center sill outboard of the truck center generally defines the width of the draft pocket. Since coupler sizes are standard for interchangeable service, the minimum inside width of the draft-pocket is generally considered to be a fixed pre-determined dimension, typically 12-⅞″. Therefore it would be advantageous to employ a draft sill of varied width, having a first, relatively wide longitudinally outboard portion in which to mount draft gear and a coupler, and a second, relatively narrower mid-span, or waist, portion between the trucks. Similarly, given that the allowable car width envelope is narrowest at mid-span, and widest at the truck centers, it may be advantageous for a portion of the deck at mid-span to be narrower than another portion of the deck either (a) closer to, or at, the truck centers; or (b) at a higher elevation at which the underframe envelope may be wider; or both.
In known center beam cars, such as those shown in U.S. Pat. No. 4,951,575 and in U.S. Pat. No. 4,802,420 of Butcher et al., issued Feb. 7, 1989, the deck structure of the cars has included inwardly tapering risers mounted above the cross bearers, with longitudinally extending side sills running along the ends of the cross-bearers. The side sills have been angle or channel sections. In U.S. Pat. No. 4,951,575 the side sills are Z-sections with the upper leg of the Z extending outward, the lower leg extending inward, and the web between the two legs running vertically. In U.S. Pat. No. 4,802,420 of Butcher et al., the side sill is a channel section, with the legs extending laterally outward and the web, being the back of the channel, extending vertically between the two legs. In both cases the winch is mounted outward of the vertical web.
It is advantageous to be able to carry loads other than, for example, bundles of lumber, on at least a part of the return journey. While this can be done with center beam cars presently in use, the overhanging wings of the top truss may tend to complicate loading of the car from above. For example, it may be more convenient to load pipe, or other objects, using an overhead crane rather than to employ side loading using a fork-lift of perhaps more limited lifting capacity. Such loading would be facilitated by removal of the top truss. Further still, in addition to removal of the top truss, truncation of the central web at a level below the bottom of the uppermost row of bundles permits the top row of bundles to be loaded side by side. Strapping for securing the load, rather than being attached to the wings of the top truss, can be carried fully over the load to the winches at deck level on opposite sides of the car. In addition, the top chord can be made wider than the posts, such that the bundles bear against the smooth outside face of the top chord at a stand-off distance clear of the flanges of the posts.
When a reduced height top chord is used, the junction of the top chord with the end bulkheads occurs at a mid-height level. This juncture may tend to act as a discontinuity, or weakness in the end bulkhead structure. Particularly when dealing with an end impact in which the load may tend to want to drive into the bulkhead, it is desirable that there be web continuity (a) between the webs of the top chord member and the vertical posts of the bulkhead member; and (b) between the web formed by the shear panel of the end-most bay and the webs of the vertical posts of the end bulkhead. In past center beam cars, the web of the end-most bay has been mounted to the leg of a vertically extending T-shaped beam, with the flange of the T-shaped member lying in the plane of the skin of the end bulkhead. When the end post of the car is a channel, or rectangular tube, the webs of the channel stand in planes lying to either side of the plane of the shear panel of the endmost bay. As described herein below, the cross-members of the bulkhead have flange continuity through the end post, such that a continuation of the web or the shear panel on the inside of the skin of the bulkhead can extend between the legs of the laterally extending cross-members. Shear can then be transferred from the shear panel into the cross-members and thence into the webs of the end post.
In center beam cars it is desirable that the main center sill be aligned with the couplers to reduce or avoid eccentric draft or buff loads from being transmitted. In dealing with lateral loads, the side sills act as opposed flanges of a beam and the floor sheets act as the web. The loads in the side sills, whether in tension, compression, vertical shear or lateral bending, tend to be transferred to the main sill through a main bolster assembly at each end of the car. In general the main bolster is located at a level corresponding to the height of the main sill, and the shear plate, if one is used, is typically at a level corresponding to the level of the upper flange of the main sill.
It is desirable to have a well deck, also called a depressed center deck or dropped deck, between the trucks, to increase the load that can be carried, and so to increase the overall ratio of loaded weight to empty weight of the car, and also to reduce the height of the center of gravity of the car when loaded, as compared to a car having a flat, straight through deck from end to end carrying the same load. In the case of a well deck, longitudinal compression and tension loads in the side sills must be carried from the level of the side sills in the well, to a second, higher level of the side sills to clear the trucks, and then through the bolster structure and into the main sill. The transmission of forces through the vertical distance of the eccentricity of the rise from the side sills height in the well to the side sill height of the end deck adjoining the bolster results in the generation of a moment. When the side sill has a knee at the transition from the well to the end structure of the car, the height of the knee defines the arm of the moment.
The coupler height of rail road cars is 34½″ above top of rail (TOR). This is a standard height to permit interchangeable use of various types of rail cars. The main sill, or stub sill if used, tends to have a hollow box or channel section, the hollow acting as a socket into which the draft gear and coupler are mounted. The minimum height of the top flange of the main sill at the trucks (or stub sill, if one is used) and the top flange of the end structure bolsters tends to be determined by the coupler height. The depth of the main bolster is limited by the need to lie high enough to clear the wheels plus a height to accommodate that portion of the coupler and draft gear about the coupler center line. At the same time, the height of the well deck is limited by the design envelope, be it Plate C, Plate F, or some other. In general, however, the rise to the height of the shear plate, or top flange of the bolster, from the well decking is less than the desired 33 inch bundle height. It is desirable for the top of the first layer of bundles stacked in the well to be at a height that permits the next layer of bundles to match the height of bundles stacked over the trucks. Consequently, it would be advantageous to have an end deck, or staging, mounted above the shear plate, or if there is no end structure shear plate, then above the bolster, at a level to match the level of the top of the bundles carried in the well between the trucks. However, increasing the height of the end deck implies an increase in the height of the knee.
One way to reduce the maximum stress at the knee is to make the side sill section of the end portion of the sill deeper. Another way to reduce the maximum stress at the knee is to make the knee member wider. On the longitudinally inwardly facing side of the knee (that is, the side oriented toward the lading in the well) the flange of the vertical leg of the knee may tend to extend perpendicularly. On the longitudinally outboard side, that is, the side facing the truck, the longitudinally outboard flange can be angled, or swept, resulting in a tapering leg, rather than one with parallel flanges. An increase in the section width, due to tapering the longitudinally outboard flange is desirable, as it may tend to permit a reduction in the maximum local stress levels in the side sill assembly at the knee, and tends to provide greater truck clearance.
When a relatively deep, relatively narrow, center sill is employed, such as in a dropped-deck center beam car having a full bundle step height, it is desirable both to discourage the center-sill from collapsing in a parallelogram manner, and to provide web continuity at the base of the center beam posts such that in terms of structural analysis, their footing may tend more closely to approximate a built-in connection, as opposed to a pin-jointed connection. Similarly, where there would otherwise be no web continuity of the cross-bearers through the center sill, such as when the cross-bearers are underslung beneath the centersill, and the cross-bearers may transmit laterally unequal loads tending to twist the center sill, it is advantageous that the center sill be discouraged from deformation in the parallelogram mode. For these reasons, is advantageous to provide internal filler braces, or webs within the center sill, and preferable to provide that bracing, or webbing, at the longitudinal stations corresponding to the locations of the webs of the vertical posts.
When the center sill is relatively deep, and narrow, installation of internal webs may challenge the skill of the fitters. It may be preferable to be able to attach at least a portion of the web from outside the center sill. That is, where either the upper, or lower flange of the center sill and the two webs have been welded together and the center sill has a high aspect ratio of depth to width, and only one flange remains to be attached, making internal welds to a gusset plate may be rather difficult. The welder may only be able to weld the portion of the gusset near to the open end of the center sill. Hence it is advantageous to provide pre-attached welding backing means, such as angles, and making welding slots in the web of the side sills at the desired gusset locations. This tends to permit the relatively inaccessible end of the gussets to be joined to the webs through a welded connection made from outside the center sill.
Torsional loads applied to the center beam assembly are transmitted through the trucks and reacted at the rails. A significant portion of this load is transferred into the deck and main sill structure at the longitudinal location of the truck center by the main posts that extend upwardly from the deck above the truck center. It may be that the main post is narrower than the center sill top cap (i.e., upper flange), and narrower than the underlying center sill webs. It such circumstances it may be advantageous to provide web and flange continuity in the center sill beneath the main post.